(1) Field of the Invention
The present invention relates to a projection view creation method, and more specifically, to a projection view creation method of creating a view by projecting a curved line to a curved surface on a two-dimensional CAD (computer aided design) system.
(2) Description of the Related Art
A CAD system is indispensable to a design job because a design specification becomes complex, a design and drawing job must be effectively carried out, a design period must be shortened and jobs accompanying the design must be simplified. The two-dimensional CAD system can optionally create drawings such as a design drawing and the like on a graphic display screen using basic figure elements such as a straight line, circle, arc and the like as well as edit created drawings. Further, when a drawing is completed on the screen, the two-dimensional CAD system can output the drawing by means of a plotter or the like and contain the created drawing in a storage medium so that it can be used later.
When the two-dimensional CAD system creates a perspective view from a plan view, front view and side view, the CAD system can display a three-dimensional configuration on a two-dimensional screen by projecting a figure observed from one direction to a figure observed from another direction. When a process for creating a view by projecting a curved line to a curved surface is carried out by the CAD system, the view is conventionally determined by an equation for calculating a shade made by the projection using equations of the actual curved surface curved line. As a result, when an element of a new configuration is added as an element desired to be projected, a unit for processing the equation of the new configuration is added so that calculation is carried out by an equation covering the additional configuration.
Nevertheless, in the conventional method of creating a view by projecting a curved line to a curved surface, since equations for expressing a curved surface and curved line are very complex, there is a problem that a program for executing a projection processing also becomes very complex. Further, since a different equation must be used to express a curved line to be projected or a curved surface to which projection is effected, there is also a problem that an exclusive program must be created in accordance with the curved line and the curved surface.